Polyurethane coatings are known for durability, toughness, and fluid resistance and have been widely used in various applications, including automotive and aerospace applications. These coatings are often formed from a multi-component composition in which one component includes one or more hydroxyl functional ingredients and another component includes one or more polyisocyanates. The components are mixed together immediately prior to use and, in many cases, can be slow to cure at ambient conditions unless accelerated with a catalyst. The presence of such a catalyst, however, significantly shortens the pot life of the combined composition. Moreover, these coatings typically require a significant induction time after the components are combined and mixed to compatibilize all of the reactive ingredients. An insufficient induction time can cause serious coating defects. With demands for higher productivity and lower cost associated with painting by original equipment manufacturers and refinishers, it is, therefore, desirable to have coating compositions that cure rapidly, have relatively long pot life, and require no induction time to form a high performance coating.
The coating of an aerospace vehicle is a multi-layer process typically including application of a substrate surface treatment, a primer coating, a colored (typically opaque) basecoat, and a transparent (typically colorless) clearcoat. Due to stringent performance requirements, such as durability and fluid resistance, the various coating layers are typically highly crosslinked and have a relatively short overcoat window, which refers to the maximum amount of time between application of coating layers before abrasion of the first layer becomes necessary for good intercoat adhesion. Overcoat windows are typically short time periods, usually varying between 12 and 24 hours depending on cure temperature. Such a short overcoat window presents a challenge when coating large objects, such as an aircraft. As a result, abrasion by sanding is a common, but undesirable, practice to get sufficient intercoat adhesion between coating layers, such as a basecoat and a clearcoat. Therefore, it is desirable to provide coatings with properties, such as durability and fluid resistance, suitable for various applications, including aerospace applications, while having a longer overcoat window.